Orientation Dependence of the Anomalous Hall Resistivity in Single Crystals of Yb₁₄MnSb_1...

The Hall resistivity, electrical resistivity and magnetization of single crystals of the tetragonal ferromagnet Yb14MnSb11 are reported as a function of the direction of the current, I, and magnetic field, H with respect to the principal crystallographic axes. With I along the unique c direction and H in the a-b plane, the anomalous Hall resistivity in the limit of zero applied field is negative for all temperatures T< Tc= 53 K. An intrinsic Hall conductivity , !xy 0, of -32 "-1 cm-1 is found for T << Tc, which decreases linearly with the spontaneous magnetization (order parameter) as the temperature is increased to Tc . In this direction, the anomalous Hall effect behaves in a manner similar to that observed in other ferromagnets such as Fe, Co, Mn5Ge3, and EuFe4Sb12. However, with I in the a-b plane and H along the c direction, the anomalous Hall behavior is completely different. The anomalous Hall resistivity data are positive for all T < Tc and a similar analysis of these data fails. In this direction, the anomalous response is not a simple linear function of the magnetization order parameter, and for a fixed temperature (T < Tc) does not depend on the magnitude of the magnetization perpendicular to the current in the a-b plane. That is, when the magnetization and applied field are rotated away from the c direction, the anomalous Hall resistivity does not change. In all other soft ferromagnets that we have examined (including La doped crystals of Yb14MnSb11, i.e. 2 Yb13.3La0.7MnSb11) rotation of the magnetization and magnetic field by an angle # away from a direction perpendicular to I results in a decrease in both the anomalous and normal portions of the Hall resistivity that approximately scales as cos(#). We suggest that the unique response exhibited by Yb14MnSb11 is a direct reflection of the delicate balance between a ferromagnetic and a non-magnetic Kondo lattice ground state